如何在PyQt4的QWidget中使用QPainter

Question

我的代码如下目前打开一个空白的500x500 QMainWindow。

我只是试图用QPainter在QWidget中绘制一个圆。

这里是我的代码：

from PyQt4 import QtCore, QtGui, Qt 
from PyQt4.QtGui import QApplication, QMainWindow 
import sys 


class Ui_MainWindow(object): 
    def setupUi(self, MainWindow): 
     MainWindow.resize(500, 500) 
     self.centralwidget = QtGui.QWidget(MainWindow) 
     self.horizontalLayout = QtGui.QHBoxLayout(self.centralwidget) 
     MainWindow.setCentralWidget(self.centralwidget) 
     self.menubar = QtGui.QMenuBar(MainWindow) 
     self.menubar.setGeometry(QtCore.QRect(0, 0, 500, 22)) 
     MainWindow.setMenuBar(self.menubar) 
     self.statusbar = QtGui.QStatusBar(MainWindow) 
     MainWindow.setStatusBar(self.statusbar) 
     QtCore.QMetaObject.connectSlotsByName(MainWindow) 

class MyMainScreen(QMainWindow): 
    def __init__(self, parent=None): 
     QtGui.QMainWindow.__init__(self, parent) 
     self.ui = Ui_MainWindow() # This is from a python export from QtDesigner 
     self.ui.setupUi(self) 

     self.paintCircle() 


    def paintCircle(self): 
     self.painter = QtGui.QPainter(self) 
     self.painter.begin(self) 
     self.painter.setPen(Qt.QPen(Qt.QColor.black)) 
     # painter.end() 
     self.painter.drawArc(QtCore.QRectF(250, 250, 10, 10), 0, 5760) 


if __name__ == "__main__": 
    app = QApplication(sys.argv) 
    mainscreen = MyMainScreen() 
    mainscreen.show() 
    app.exec_() 

，我发现了以下错误：

QPainter::begin: Paint device returned engine == 0, type: 1 
QPainter::begin: Paint device returned engine == 0, type: 1 
QPainter::setPen: Painter not active 

Answer 1

您必须重写paintEvent功能，在您的情况：

from PyQt4 import QtCore, QtGui, Qt 
from PyQt4.QtGui import QApplication, QMainWindow 
import sys 


class Ui_MainWindow(object): 
    def setupUi(self, MainWindow): 
     MainWindow.resize(500, 500) 
     self.centralwidget = QtGui.QWidget(MainWindow) 
     self.horizontalLayout = QtGui.QHBoxLayout(self.centralwidget) 
     MainWindow.setCentralWidget(self.centralwidget) 
     self.menubar = QtGui.QMenuBar(MainWindow) 
     self.menubar.setGeometry(QtCore.QRect(0, 0, 500, 22)) 
     MainWindow.setMenuBar(self.menubar) 
     self.statusbar = QtGui.QStatusBar(MainWindow) 
     MainWindow.setStatusBar(self.statusbar) 
     QtCore.QMetaObject.connectSlotsByName(MainWindow) 


class MyMainScreen(QMainWindow): 
    def __init__(self, parent=None): 
     QtGui.QMainWindow.__init__(self, parent) 
     self.ui = Ui_MainWindow() # This is from a python export from QtDesigner 
     self.ui.setupUi(self) 

    def paintEvent(self, event): 
     painter = QtGui.QPainter(self) 
     painter.setPen(QtGui.QPen(QtCore.Qt.red)) 
     painter.drawArc(QtCore.QRectF(250, 250, 10, 10), 0, 5760) 

if __name__ == "__main__": 
    app = QApplication(sys.argv) 
    mainscreen = MyMainScreen() 
    mainscreen.show() 
    app.exec_() 

输出：

Answer 2

你必须使用名称

def paintEvent(self, event): 

，而不是def paintCircle(self):自动运行它何时需要。

from PyQt4 import QtCore, QtGui, Qt 
from PyQt4.QtGui import QApplication, QMainWindow 
import sys 

class Ui_MainWindow(object): 

    def setupUi(self, MainWindow): 
     MainWindow.resize(500, 500) 
     self.centralwidget = QtGui.QWidget(MainWindow) 
     self.horizontalLayout = QtGui.QHBoxLayout(self.centralwidget) 
     MainWindow.setCentralWidget(self.centralwidget) 
     self.menubar = QtGui.QMenuBar(MainWindow) 
     self.menubar.setGeometry(QtCore.QRect(0, 0, 500, 22)) 
     MainWindow.setMenuBar(self.menubar) 
     self.statusbar = QtGui.QStatusBar(MainWindow) 
     MainWindow.setStatusBar(self.statusbar) 
     QtCore.QMetaObject.connectSlotsByName(MainWindow) 

class MyMainScreen(QMainWindow): 

    def __init__(self, parent=None): 
     QtGui.QMainWindow.__init__(self, parent) 
     self.ui = Ui_MainWindow() # This is from a python export from QtDesigner 
     self.ui.setupUi(self) 

    def paintEvent(self, event): 
     self.ui.centralwidget.painter = QtGui.QPainter() 
     self.ui.centralwidget.painter.begin(self) 
     self.ui.centralwidget.painter.setPen(QtGui.QPen(QtCore.Qt.red)) 
     self.ui.centralwidget.painter.drawArc(QtCore.QRectF(250, 250, 10, 10), 0, 5760) 
     self.ui.centralwidget.painter.end() 

if __name__ == "__main__": 
    app = QApplication(sys.argv) 
    mainscreen = MyMainScreen() 
    mainscreen.show() 
    app.exec_() 

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例子draw on canvas